Disproportionation/transalkylation of aromatic hydrocarbons

Abstract

A catalyst for the disproportionation / transalkylation of various hydrocarbons consists of a carrier and a metal component supported on the carrier. The carrier comprises 10 to 80 wt % of mordenite and / or beta type zeolite with a mole ratio of silica / alumina ranging from 10 to 200; 0 to 70 wt % of ZSM-5 type zeolite with a mole ratio of silica / alumina ranging from 30 to 500; and 5 to 90 wt % of at least one inorganic binder selected from the group consisting of gamma-alumina, silica, silica alumina, bentonite, kaolin, clinoptilolite, and montmorillonite. The metal component comprises platinum and either tin or lead. The catalyst enables mixed xylenes to be produced at remarkably high yields from benzene, toluene and C9 or higher aromatic compounds through disproportionation / transalkylation with a great reduction in aromatic loss. In addition, the catalyst can maintain its catalytic activity for a long period of time without deactivation.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates, in general, to a catalyst for the disproportionation / transalklylation of aromatic hydrocarbons and, more particularly, to a catalyst which is useful to prepare mixed xylenes from a mixture of benzene, toluene and C9 or higher aromatic compounds through disproportionation / transalklylation. Also, the present invention is concerned with a method for preparing such a catalyst.2. Description of the Prior ArtMixed xylenes, very important raw materials in the petrochemical industry, are composed of ethyl benzene and xylene isomers including meta-xylene, para-xylene and ortho-xylene. From mixed xylenes, thus, pure m-xylene, p-xylene and o-xylene, all important base fractions in the petrochemical industry, can be produced.Owing to their similar boiling points, xylene isomers are very difficult to individually extract from the mixed xylenes by ordinary distillation processes. Usually, adsorptive separation, cry...

AI Technical Summary

Benefits of technology

The intensive and thorough research on the development of a catalyst for the disproportionation / transalkylation of aromatic hydrocarbons, repeated by the present inventors aiming to solve the problems, resulted in the finding that platinum, together with tin or lead which plays a role as a controller of the high hydrogenating activity of platinum, is capable of producing mixed xylenes at high yields and exceptionally preventing the catalyst deactivation when being supported on a carrier consisting of mordenite or beta type or ZSM-5 type zeolite and an inorganic binder.

Problems solved by technology

Owing to their similar boiling points, xylene isomers are very difficult to individually extract from the mixed xylenes by ordinary distillation processes.

From a reaction containing C9 or higher aromatic hydrocarbons, however, a high yield of the mixed xylenes cannot be expected because the reaction is hard to dealkylate with the catalyst.

However, the weakening of the acidity without the introduction of a hydrogenating metal results in deteriorating the catalytic activity of the catalyst and thus, reducing the yield of the mixed xylenes.

However, it is expected that this catalyst becomes deactivated faster during the catalytic reaction than does the catalyst employing activity-controlled platinum because the hydrogenation activity of nickel is far poorer than that of platinum.

In addition, when sulfur compounds are introduced into the reaction, the hydrogenation activity of the nickel is greatly deteriorated owing to its strong association with the sulfur compounds.

The feedstocks, which are fed into the commercial disproportionation / transalkylation process, usually undergo desulfurization in advance, but there is not completely excluded the possibility that sulfur compounds might flow into the disproportionation / transalkylation process owing to process accidents or operational errors.

In the case of nickel, the sulfur compounds, if adsorbed once, are very difficult to remove during reaction.

In this case the anti-deactivation effect cannot be efficiently conducted when the reaction contains C10 aromatic hydrocarbons or a high proportion of C9 aromatic hydrocarbons.

When the reaction gets a high content of C9 or higher aromatic hydrocarbons, the catalyst is difficult to protect from deactivation.

In addition, the presence of sulfur compounds in the reaction may make the hydrogenating activity of the catalyst drop to an unrecoverable state.

The use of ZSM-5 type zeolite alone, however, can be applied for toluene only, but cannot be applied for the disproportionation or transalkylation of C9 or higher aromatic hydrocarbons because of its structural limit.

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